As a related-art bearing device for a wheel, for example, there is proposed a bearing device for a wheel, which is configured so that a hub wheel is separable from an outer joint member of a constant velocity universal joint to attain excellent maintainability (see, for example, Patent Document 1). As illustrated in FIG. 9, the bearing device for a wheel as disclosed in Patent Document 1 includes, as main components thereof, a fixed type constant velocity universal joint 107, and a bearing 106 for a wheel including a hub wheel 101, an inner ring 102, double-row rolling elements 103 and 104, and an outer ring 105.
The hub wheel 101 has an inner raceway surface 108 on an outboard side formed on an outer peripheral surface thereof, and includes a wheel mounting flange 109 configured to allow a wheel (not shown) to be mounted thereto. Hub bolts 110 configured to fix a wheel disc are equiangularly embedded in the wheel mounting flange 109. The inner ring 102 is fitted to a small-diameter step portion 111 formed on an outer peripheral surface of the hub wheel 101 on the inboard side, and an inner raceway surface 112 on the inboard side is formed on an outer peripheral surface of the inner ring 102.
The inner ring 102 is press-fitted with an adequate interference for the purpose of preventing creep. The inner raceway surface 108 on the outboard side that is formed on the outer peripheral surface of the hub wheel 101 and the inner raceway surface 112 on the inboard side that is formed on the outer peripheral surface of the inner ring 102 correspond to double-row inner raceway surfaces. The inner ring 102 is press-fitted to the small-diameter step portion 111 of the hub wheel 101, and the end portion of the small-diameter step portion 111 is staked outward. As a result, the inner ring 102 is retained by a staked portion 113 thus formed and integrated with the hub wheel 101, to thereby apply preload to the bearing 106 for a wheel.
The outer ring 105 has double-row outer raceway surfaces 114 and 115 formed on an inner peripheral surface thereof so as to be opposed to the inner raceway surfaces 112 and 111 of the hub wheel 101 and the inner ring 102. An outer peripheral surface of the outer ring 105 is fitted and fixed to a knuckle extending from a suspension device (not shown) of a vehicle body, and thus the bearing device for a wheel is mounted to the vehicle body.
The bearing 106 for a wheel has a double-row angular contact ball bearing structure. Specifically, the rolling elements 103 and 104 are interposed between the inner raceway surfaces 108 and 112 formed on the outer peripheral surfaces of the hub wheel 101 and the inner ring 102 and the outer raceway surfaces 114 and 115 formed on the inner peripheral surface of the outer ring 105, and the rolling elements 103 and 104 in the respective rows are equiangularly supported by cages 117 and 118.
In opening portions of the bearing 106 for a wheel at both ends thereof, a pair of seals 119 and 120 configured to seal annular spaces between the outer ring 105 and the hub wheel 101 and between the outer ring 105 and the inner ring 102 is fitted to a radially inner part of the outer ring 105 at both end portions thereof. The seals 119 and 120 prevent leakage of grease filled inside and entry of water and foreign matter from the outside.
The constant velocity universal joint 107 includes an outer joint member 123 being arranged at one end of an intermediate shaft 121 serving as a drive shaft and having track grooves 122 formed in an inner peripheral surface thereof, an inner joint member 125 having track grooves 124 formed in an outer peripheral surface thereof so as to be opposed to the track grooves 122 of the outer joint member 123, balls 126 assembled into spaces between the track grooves 122 of the outer joint member 123 and the track grooves 124 of the inner joint member 125, and a cage 127 interposed between the inner peripheral surface of the outer joint member 123 and the outer peripheral surface of the inner joint member 125 so as to retain the balls 126.
The outer joint member 123 includes a mouth section 128 configured to accommodate internal components such as the inner joint member 125, the balls 126, and the cage 127, and a stem section 129 integrally extending from the mouth section 128 in an axial direction. An axial end of the intermediate shaft 121 is press-fitted to the inner joint member 125, and is coupled by spline fitting so as to allow torque transmission therebetween.
A bellows-like boot 130 made of a resin is mounted between the outer joint member 123 of the constant velocity universal joint 107 and the intermediate shaft 121 so as to prevent leakage of a lubricant such as grease filled inside the joint, and to prevent entry of foreign matter from outside the joint, thereby attaining a structure of closing an opening portion of the outer joint member 123 with the boot 130. The boot 130 includes a large-diameter end portion fixed to an outer peripheral surface of the outer joint member 123 by fastening with a boot band, a small-diameter end portion fixed to an outer peripheral surface of the intermediate shaft 121 by fastening with a boot band, and a flexible bellows portion connecting the large-diameter end portion and the small-diameter end portion and being reduced in diameter in a range of from the large-diameter end portion toward the small-diameter end portion.
A male spline including a plurality of convex portions 132 extending in the axial direction is formed on an outer peripheral surface of the stem section 129 of the outer joint member 123 (see FIG. 10 and FIG. 11). On the other hand, a simple cylindrical portion 134 having no female spline formed thereon is formed on an inner peripheral surface of a shaft hole 133 of the hub wheel 101 (see FIG. 10 and FIG. 12). In this bearing device for a wheel, as illustrated in FIG. 9 and FIG. 10, under a state in which the stem section 129 of the outer joint member 123 is press-fitted to the shaft hole 133 of the hub wheel 101, a bolt 138 is threadedly engaged with a female thread 137 formed at an axial end of the stem section 129 of the outer joint member 123, and is fastened in a state of being locked on an end surface of the hub wheel 101, to thereby fix the constant velocity universal joint 107 to the hub wheel 101.
To press-fit the stem section 129 of the outer joint member 123 to the shaft hole 133 of the hub wheel 101, the shape of each convex portion 132 of the stem section 129 is transferred to the inner peripheral surface of the shaft hole 133 of the hub wheel 101. Thus, as illustrated in FIG. 13 and FIG. 14, concave portions 136 brought into close contact with the corresponding convex portions 132 with interferences therebetween are formed on the inner peripheral surface of the shaft hole 133 of the hub wheel 101, to thereby define a convex and concave fitting portion N (see FIG. 9) in which close contact is achieved at an entire fitting contact portion therebetween. As a result, the outer joint member 123 and the hub wheel 101 are coupled to each other so as to allow torque transmission therebetween.